National Aeronca Association Bulletin Board

...I had plans of flying my Champ several months and then...new Spars and covering, but I'm considering "taking it down" now. My question is, we have a Specialty Wood company here in town that handles Mast-n-Beam Vertical Grain Spruce. I know of at least 2 Champ guys to use them. At less than $500. for all 4 blanks, they'll surface 3 sides to specs. (4th side to be beveled). ...any opinions? What's the rules for wood spars, do you need to "record" of where you got them from? Do you normally get "papers" when purchasing them? Do they need to be stamped "PMA"? thanks, Jim

Hi Jim,

Go for it, sounds like a great deal on spars. AC43.13 is the rule book for all things Airplane, and Chapter 1 is all about wood. Factory documents would also be acceptable. I believe Todd Tainer has a blueprint of the spars on his website: drawings 5-146 and 5-147. Check here.

The main things to look at when selecting wood are; grain slope (no more than 1:15), rings per inch (15 rings I think), and defects. Edit: 6 Rings per inch is all that is required. Chances are, if 2 other airplanes have already used them, the selection of wood will be very good. But to be on the safe side, you and/or a knowledgeable A/P should pick the blanks to assure acceptable wood.

As for "Records” their really aren't any. It is considered an "Owner Produced Part" because you are directing and overseeing the manufacturing of the product. But the more information you keep in the logs, the better. Simply list the supplier, what they did, and the date; that should be sufficient.

Same with "Papers"; most likely all you'll get is an invoice that they cut X feet of wood and finished 3 sides.

No PMA stamp needed, falls under 'Owner Produced Part.'

Only other words of advise: Keep your A/P IA in the loop. Invite him over for a beer and show him your work when ever you do something important. This allows him to see the project as it moves along. It will make him feel much better and more confident when sign off time comes. After all, it's your work, but HIS signature and HIS liability to release the airplane back into service.

nkh

Agree with Nathan but I would get together with your A&P/IA about this now, and tell him what you are planning. He will probably go with you to the shop and look at the wood before approving it.

Getting a copy of the blueprint from Todd or NAA's Brian Matz is mandatory as you will need to give a copy to the people who cut the wood out in the beginning. Give them your limitations (no knots etc) and go from there.

Great to find a local source and keep us in the loop on how it goes.

Joe

I Love This Site, ....Nate, I borrowed an earlier copy of AC 43.13 from someone, thanks for the info. I'm waiting for my local Aviator shop to open so I can pickup my own current copy.
2 more questions, please.
First, I didn't see any mention of (15) Rings per inch, is that max or min? Second, with respect to Glue, what's all around best, ...Plastic Resin (most popular) or Resorcinol (most water resistant)? I'm in Houston, if ya'll think it makes a difference. thanks again, Jim

Joe, I did view Todd's drawings, it's great to have that kind of stuff, the info is priceless and I did send him "a-few-bucks".

JK,

Let me save you a "few bucks" so to speak.

Google AC43-13 and you will find that you can download the entire publication from the FAA for free!

Joe

Joe, ...you da man! ...it's done.
PS: the store's still not open, I didn't have to get out of my PJ's and it didn't cost anything, ...what a deal! thanks, Jim

wha da ya'll think about the Glue (question above)?

Jim,

Now you can use that few bucks you just saved for something important.

When we send NAA renewals around you can use the money there!

Joe

Jim,

I can't seem to find anything in writing about the 15 rings per inch. Maybe that's my "Old School" teachings coming out. It use to be, when Old-Growth spruce was the norm, 15 rpi was the minimum for use on Spars. But when I look at the Aircraft Spruce Catalog, they say "No fewer than six annular rings per inch" , and AC43.13 doesn't mention anything. So obviously something has changed (most likely 30 years ago ) maybe because Old-Growth is hard to find these days. Long story short.... scrap the 15 and use 6 rings per inch minimum.

As for glue; I'm old fashion and still use Resorcinol. I have never seen a properly made glue joint fail, with this stuff. Sure it may look ugly to some, because it's a dark brown and oozes out of the joints, but I like it. With all the shrinking and expanding wood does, Resorcinol handles it very well since it's only resin and saw dust. And it's the cat's meow when it comes to moisture. 15 minutes in boiling water doesn't hurt it any, so I'd say it can handle the humidity of the south for 50-60 years. Be sure to mix it by Weight and not Volume; you’ll get better results. Make a test piece with each batch, and break it after it cures. And it cleans up very easily with water (before it cures), keep a moist rag handy to wipe away the ooze-izge. Keep in mind, Resorcinol has been around a LONG time. It started off as a boat builder’s glue, and when airplane builders realized Caseins glue (made from horse parts) would fail after several years, they switch over Resorcinol.

I have nothing against Plastic Resin, except it's somewhat new and doesn't have the track record of Resorcinol. When it's been approved for 50 years, and they haven't had a problem, then maybe I'll start using it.

Once again though, it comes down to what your A/P IA is comfortable with.

nkh

I am totally amazed that you can buy your own wood and produce an approved spar for a certified plane. I am assuming the A&P submits a 337 for this but from the horror stories I've heard about when doing even minor alterations I can just see the FAA guys laughing when I take the paperwork to them. I can see this in my future so I am very interested in the outcome and learning how to get this approved.
I'm sending in my dues Monday!!!!!

Jim in Arkansas 2121E

Hi Jim,

You're really close; your AP will get his IA (or himself if he's got an IA) to approve the spar replacement in this situation. The FAA has no say in this matter.

Here's how it works: Form 337's are kinda like a 'cover sheet' for major alterations or repairs. It's there to document any change on the aircraft. It's the IA job to approve or decline the alteration or repair. Once he approves it, that's the end and the form is sent to the FAA in Okalahoma City to be put in the aircrafts file. (If you call the FAA, you can get a copy of the file on CD format. It will have every 337, Bill of Sale and any other piece of paper the FAA has on your airplane.)

Now if you do a major Alteration in the true form of the word; like add an extra wing, or a different engine not listed on the TSDC, or clip the wings for example; then the FAA gets involved in the approval. The form is sent to the FAA, who hands it over to their 'Aircraft Certification Office' (ACO). ACO will look over the alteration from an engineering standpoint by trained engineers and approve / decline it. This is often referred to as a "One-Time STC" and can be a little time consuming. Anywhere from 2 weeks too 2 months for an answer. (This is where everyone is complaining.)

Way back when.... the local FAA man (FISDO / GADO) would actually come look at the airplane when you made an Alteration / Repair to approve it. This was referred to as a "Field Approval." But for some reason, the FAA has phased out Field Approvals and refer everything to ACO.

If you're amazed by making spar's, this will blow your mind away.... Do to the 'Owner/Operator Produced Parts' clause; you can make any part of an airplane. Anything from the fuselage to fabric as long as you can prove it meets or exceeds the original specs. Because of this clause, old airplanes will never go away, at least not do to unattainable parts.
Pretty cool!

nkh

Thanks for the education, I really appreciate the help in understanding what can be done to keep my plane flying. The wind has died down to a slight cross wind so off I go to practice my landings.
Later
Jim in Arkansas